Ignition System: Testing and Inspection
Electronic Ignition System Diagnosis
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions)provides an overview of each diagnostic category.
Circuit/System Description
This ignition system uses individual ignition module/coil assemblies for each cylinder. The engine control module (ECM) controls the spark events by transmitting the timing pulses on the ignition control (IC) circuits to the individual ignition module/coil assemblies in firing order sequence. Each ignition module/coil has the following circuits:
* Ignition voltage
* Ground
* Ignition Control (IC)
* Low reference
Diagnostic Aids
* Depending on location in the spliced ignition voltage circuit, a slight resistance can cause a misfire or a crank/no start condition. A voltage drop test on the circuit will pinpoint this condition.
* A slight to moderate resistance on any IC circuit can cause a misfire before DTC P0351-P0358 sets.
* Extended engine cranking time may foul the spark plugs with excessive fuel.
* When disconnecting electrical connectors or removing fuses and relays from a fuse block, always inspect both mating electrical terminals for corrosion and terminal tightness.
* Use the J 35616 for any test that requires probing the underhood fuse block terminals, component wire harness terminals, or the ECM wire harness terminals.
Reference Information
Schematic Reference
Engine Controls Schematics ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning)for scan tool information
Special Tools
* J 26792 Spark Plug Tester
* J 35616-A/BT-8637 Connector Test Adapter Kit
Circuit/System Verification
1. Verify that the engine is in good mechanical condition before continuing with this diagnostic.
2. Verify the following conditions:
* The ignition coils/modules are correctly wired and connected
* The proper firing order
* The proper spark plug type
* The proper spark plug gap and torque
* The proper ohm values for the spark plug wires
Refer to Ignition System Specifications (Application and ID) and Spark Plug Inspection (Testing and Inspection).
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the affected ignition coil/modules.
2. Ignition OFF for 90 seconds, test for less than 5 ohms between the ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
3. Test for less than 5 ohms between the low reference circuit terminal B and ground.
• If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
Important: If the ignition fuse is open, it will be necessary to test the spliced ignition circuits and the components for a short to ground.
4. Ignition ON, verify that a test lamp illuminates between the ignition voltage circuit terminal D and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
5. Exchange the affected ignition coil/module with the ignition coil/module of a good cylinder.
6. Start the engine and observe the scan tool Misfire Current Cylinder parameters.
• If the misfire transfers with the suspect ignition coil/module, replace as needed.
7. If the circuits test normal, test or replace the spark plugs.
Component Testing
Use the J 26792 to verify the output of each ignition module/coil.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Engine Control Module Programming and Setup (LF1) (Testing and Inspection)Engine Control Module Programming and Setup (LLT) (Testing and Inspection)Engine Control Module Programming and Setup (V8) (Testing and Inspection)
* Engine Control Module Replacement (Service and Repair)
* Ignition Coil Replacement (Service and Repair)
* Spark Plug Replacement (Service and Repair)